Trolleys with castor wheels are generally heavy and unwieldy to steer and are particularly difficult to control when they are loaded. Manoeuvring a trolley utilising the hand rail provided at the rear of the trolley is no easy task, and involves a certain degree of dexterity and strength from the arm, waist and back of the user.
Users often find themselves in circumstances where they need to change the direction of travel of the trolley frequently such as when manoeuvring a shopping trolley along an aisle in a supermarket. The same applies to trolley beds in hospitals and serving trolleys in restaurants and bars. When turning a trolley from standstill, the user effectively acts as the pivot about which the trolley is moved. As the front castor wheels are relatively distant from the user, a significant torsional force from the waist and lower back of the user is required in order to turn the trolley from standstill or to swing it around from the direction it is pointing. The force required for this is substantially increased when the trolley is loaded. As a result, lower back injuries and muscle strain are relatively common. The resulting muscle pain and discomfort may not be immediate, but may become apparent hours or days after trolley usage. In severe cases, muscle injuries resulting from trolley usage may exacerbate existing muscle or spine injury and in some cases, can be debilitating.
Another awkward situation in which users quite frequently find themselves is when pushing a trolley across a sloping or uneven surface. More specifically, it is not uncommon for a trolley to stall or for the user to lose control of the trolley when the front castor wheels of the trolley are driven into a bump. Trolleys are also inherently susceptible to turning down a sloping surface. In either instance, the user is forced to exert a significant effort in order to maintain the trolley on track. In the latter instance in particular, the user must exert a constant torsional force from their back region to prevent the trolley from turning from the direction of travel while traversing the sloping surface, which again subjects the user to increased risk of back and muscle injury.
The castor wheels of shopping trolleys are also notorious for swivelling from side to side when being pushed over rough surfaces such as often found on footpaths and in supermarket car parks, which besides being an annoyance, impacts deleteriously on the control the user has on the trolley.
Patents and patent applications EP424234 (Guitel Etienne Mobilor), JP10166807 (Nanshin KK), EP0370716 (Herok RJK), WO9325398 (Lloyd Gerald), and GB2389084 (Moye Cyril) describe castors designed to address these problems. The castors described by these patents and patent applications each have a component in frictional contact with the wheel which urges a lock into engagement upon rotation of the wheel in a forward direction, and out of engagement upon rotation in a reverse direction. The lock prevents the castor swivelling.
Although each of these castors can be locked and unlocked they have considerable operational limitations. When the castors' swivel is locked and the locked castors are guiding the trolley a considerable and variable side pressure is applied to the lock. The unlocking force applied to the lock of each of these castors is not necessarily adequate to provide immediate and consistent unlocking in normal operational situations.
Furthermore, the castor of Patent WO9325398 (Lloyd Gerald) enables an operator to unlock the castor swivel by a sideways movement of the trolley. This arrangement has the disadvantage that the castor may be unintentionally unlocked during normal operation. The castors may, for example, be unlocked when a trolley is maneuvered across a slope or steered under load. When using this castor an operator cannot be sure that the swivel will remain locked in all operational situations and allow the guidance wheel to perform appropriately.
Patent JP55156702 (Morita) describes a castor that has considerable disadvantages. A component of the castor that is in frictional contact with the wheel rotates. The rotating component is also in frictional contact with a slide which locks and unlocks the swivel. Because of the frictional contact and relative movement between the rotating component and the sliding component it is almost impossible for them to remain synchronized.
Patent GB2106378 (Morita) also describes a castor which has a component in frictional contact with the wheel. The component brakes the wheel when it rotates in a reverse direction. The braking action of the component pivots a sub-bracket to which the wheel is mounted. This pivotal movement unlocks the swivel. This approach has considerable disadvantages including the number and complexity of the components. Furthermore, because the wheel is mounted to the sub-bracket and not to the castor frame as is normally the case the components of this need to be quite strong.